The most popular N scale buildings can vary depending on personal preferences of model train enthusiasts, the era and geographic location they are modeling, and the layout theme. However, there are a few manufacturers that are well-known for producing high-quality N scale structures that are popular among model railroaders.

One of the most popular N scale building manufacturers is Faller, a German company that produces a wide variety of structures ranging from houses and shops to industrial buildings and train stations. Their kits feature high-quality details and realistic textures, and they offer a wide variety of styles that can fit different themes and eras.

Another popular N scale building manufacturer is Kibri, also a German company. Kibri produces a range of structures including houses, factories, bridges, and other buildings. Their kits feature detailed, realistic architecture and textures, and they are known for their accuracy and attention to detail.

Other popular N scale building manufacturers include Woodland Scenics, Walthers, and Model Power. These companies produce a wide variety of structures, including houses, stores, factories, and other industrial buildings.

Ultimately, the most popular N scale buildings depend on individual preferences and the specific needs of a model railroad layout. Model train enthusiasts often choose structures that match the theme and era of their layout, as well as their personal tastes and interests.

There are also lots of independant small N Scale building manufacturers and producers that sell special buildings like "Small Town 3D Models". These smaller creators don't mass produce buildings and kits like the companies above.  The quality can be better also due to small batch production of models and the rise of 3D printing (when done correctly).

There are a lot of people out there creating "not so good" 3D printed models for train layouts and these sub par models give 3D printed train models a bad name in some cases.  If done correctly, 3D printed buildings and scenery quality can rival or even be better than comerically produced models, printed with tons of detail and accuarcy.  

And speaking of accuracy, a lot of the commercially produced buildings are not as accurate as they should be.  A lot of commercial producers of N Scale buildings seem to make their buildings a bit larger in scale than they should be.  I have run into this way too many times. I guess the commercial companies are trying to use thier models for more than one scale it seems.

So you have a lot of choices when it comes to buildings and scenery for your N Scale Train Layout.  Just try checking out the "little guys" on places like Etsy and such for some gems when it comes to N Scale buildings and scenery.